Astronomers have found the most distant evidence of water in the Universe, a major conference has been told.
The vapour is thought to be present in a jet ejected from a supermassive black hole at the centre of a galaxy that is billions of light-years away.
The discovery, by a US-European team, was announced at the European Week of Astronomy and Space Science meeting.
The water was emitted from the black hole when the Universe was only about 2.5 billion years old.
This is about one fifth of the Universe’s current age, astronomers say. The water’s signature, seen at radio wavelengths, is only now being detected because of the huge distance in space between the black hole and Earth.
The vapour is observed as a “maser”, in which molecules in the gas amplify and emit beams of microwave radiation.
“We have been observing the water maser every month since the detection and seen a steady signal with no apparent change in the velocity of the water vapour in the data we’ve obtained so far,” said Dr John McKean of the Netherlands Institute for Radio Astronomy.
“This backs up our prediction that the water is found in the jet from the supermassive black hole, rather than the rotating disc of gas that surrounds it.”
The faint signal was detected using a technique called gravitational lensing.
This is where the gravity of a massive galaxy in the foreground acts as a cosmic telescope, bending and magnifying light from the more distant galaxy.
“The radiation that we detected has taken 11.1 billion years to reach the Earth,” explained Dr McKean.
“However, because the Universe has expanded like an inflating balloon in that time, stretching out the distances between points, the galaxy in which the water was detected is about 19.8 billion light years away.”